1. Field of the Invention
The present invention relates to an apparatus adapted to inspect a pattern on a substrate and a related method. More particularly, the invention relates to a method and apparatus adapted to inspect a pattern characteristic using a statistical inference function using a light signal corresponding to the pattern characteristic.
This application claims the benefit of Korean Patent Application No. 2004-66203 filed on Aug. 23, 2004, the subject matter of which is hereby incorporated by reference in its entirety.
2. Description of the Related Art
As semiconductor devices have become more highly integrated and operating speeds have increased, design rules have changed. In general, a contact area and other critical dimensions defining the layout of contemporary semiconductor devices have gradually been reduced. These even smaller dimensions are increasingly intolerant to design and manufacturing errors. Yet, such ever smaller defects are harder and harder to identify during quality assurance processes. For example, common processing defects include voids formed in an insulation interlayer and a bridge defect formed on the contact plug of a stacked capacitor structure. As the overall dimensions of these individual components have shrunk over time, the associated processing defects have become ever more small and difficult to locate.
Most processing defects are caused by a pattern defect. Hence, each thin layer formed by a unit process step during the manufacture of a semiconductor device must be inspected for the presence of pattern defects. For example, the thickness of a thin layer formed on a substrate must be inspected following a deposition process. The thickness and/or width of a substrate pattern must similarly be inspected following a photolithography process. Where an inspected thickness or width is determined to be outside the allowed error tolerance, the process conditions associated with the unit process are often changed to prevent the subsequent formation of additional processing defects.
A scanning electron microscope (SEM) measurement or an optical measurement is widely utilized in pattern inspection processes.
A conventional SEM measurement technique typically involves direct examination of a substrate portion (hereafter the “specimen”) including the pattern to be inspected. To do this, an electron beam is projected onto a cross sectional surface of the specimen, and secondary electrons are discharged from the specimen. The discharged secondary electrons are detected by the SEM, and the SEM provides a corresponding two dimensional image of the specimen, or the inspection pattern. This image is often referred to as a vertical profile of the inspection pattern. The physical properties of the inspection pattern such as a thickness, a width and a height are directly measured from the vertical profile of the inspection pattern. From the physical properties determined by the SEM measurement, a direct determination may be made as to whether or not the measured physical properties meet design specifications (e.g., fall within error tolerances).
Unfortunately, the SEM measurement requires a vacuum state and a lengthy examination period in order to provide satisfactory inspection results. The slow rate of inspection provided by SEM measurements is particularly disadvantageous in the context of modern manufacturing facilities which require highly efficient processes in order to ensure commercially viable productivity.
A conventional optical measurement technique typically involves periodically irradiating a surface portion of a substrate containing the desired inspection pattern, and detecting an optical signal reflected from the inspection pattern using an optical detector. The reflection optical signal is thereafter analyzed by the complex combination of a matrix function and an electromagnetic function to determine the physical properties of the inspection pattern and to estimate whether or not the obtained physical properties are within the allowable tolerance limits.
The conventional optical measurement technique provides fairly accurate results where the inspection pattern is formed with a relatively simple, two-dimensional matrix shape. However, the conventional optical measurement technique has a great difficulty analyzing the large number of reflected optical signals generated by more complicated inspection patterns. Indeed, such analysis typically requires the use of a costly computer server to process a large number of complex, reflected optical signals.
Thus, the two most common techniques used to detect pattern defects require an examination of the physical properties of the inspection pattern. Yet, an accurate measurement of the physical properties of an inspection pattern is not necessarily required for the detection of pattern defects, and further reliance on the examination of physical properties will only become ever more fruitless as pattern designs are defined in smaller and smaller dimensions. For these reasons, ongoing research continues into the problems associated with pattern defect inspections and the proper formation of patterns on semiconductor devices.
For example, Japanese Patent Laid-Open Publication No. 2002-261139 discloses a method of forming a pattern with optimal thickness or width by optimally varying the processing conditions during a unit process in accordance with variations in the amount of light reflected from the surface of an inspection pattern.
Unfortunately, this disclosure has a problem in that the optimal reflection light and the optimal pattern have no unique correspondence with each other, since an accurate statistical analysis correlating the reflection light and physical properties of the inspection pattern are not usually known.
Additionally, Japanese Patent Laid-Open Publication No. 2001-330421 discloses a method of inspecting a pattern using a surface ratio for the pattern with respect to the underlying substrate. That is, the surface ratio is obtained by relating a detection pulse derived from a light reflected from the surface of the inspection pattern and an output pulse derived from a source light irradiating the substrate. Yet, unfortunately, this disclosure has limited utility to only those inspection patterns having clear periodic features repeated across the substrate since the surface ratio of the inspection pattern is obtained from the ratio of the inspection pulse with respect to the output pulse. Accordingly, the inspection method proposed in this Japanese laid-open patent document cannot be applied to inspection patterns lacking such periodic features.
These disclosures are but two examples of the many inadequate attempts previously made to develop an improved method of inspecting for defects in an inspection pattern without the requirement of accurately measuring the physical properties of the inspection pattern.